All 10 companies that debuted on the U.S. public markets this week either sold fewer shares than initially planned, accepted a lower-than-expected price, or both. The recent selloff in high-growth pockets of the market has made some investors turn more conservative as a wave of new companies hit the market.

Some 83% of companies that went public over the past three months weren’t profitable, just shy of the all-time record in the first quarter of 2000, when 84% of new public companies were money-losers, according to Jason Goepfert, founder of Sundial Capital Research and author of the SentimenTrader Daily Report. His methodology looks for companies that had negative net income on a quarterly basis prior to the announced IPO.

For instance the unprofitable Zoe's Kitchen, which started trading on the public markets last Friday, has doubled from its $15 IPO price.

Such a high percentage of unprofitable companies going public doesn’t necessarily bode well for the U.S. stock market in the months ahead. In March 2000, when IPOs by unprofitable companies were reaching their all-time record by Goepfert’s calculation, the Nasdaq Composite peaked before tumbling into a deep bear market as the dot-com bubble burst.

When the percentage of money-losers going public has been greater than 70% of total IPOs, the S&P 500 has averaged a 4.2% decline over the next 12 months, according to Mr. Goepfert, whose data go back to 1998. By comparison, when this percentage of money-losing companies going public was less than 25% of IPOs, the S&P 500 averaged an 18% gain over the next 12 months.

“With any business deal, it’s wise to consider why someone is willing to sell what you’re buying,” Mr. Goepfert said. “With company founders, investment bankers and private equity firms lining up to sell the public shares in firms that can’t make a dime, the public would be wise to step back and ask “why?”

The performance isn’t surprising: Young companies are usually more willing to go public in an environment where the stock market is rallying and they are more likely to see a pop in their stock. By comparison, the IPO market nearly dried up in March 2009, when stocks were in free-fall and there appeared to be little hope on the horizon. Hindsight is 20-20, of course, as stocks rebounded sharply off the March 2009 low.

“Bankers have been aggressive in meeting the public’s appetite for the chance at a quick pop in a new listing’s offering,” Mr. Goepfert said about the recent listings.

Whether investors are still hungry, and just what it means for the overall market, are the big questions going forward.